Current research activities

This page gives a short description of the different research activities, to quickly jump to a specific work use the link list below.
If you are interested in a particular topic and would like to know more, please feel invited to contact
the person(s) listed with this topic.

The development of efficient quantum computational methods is a crucial aspect in the development of the
new generation devices where the size of the charge confinement becomes comparable to the electron wavelength.
We are interested in studying semiconductors where the heterostructure design induces coherent interference
effects between different bands. We will investigate the contribution of interband current in a Resonant
Interband Tunneling Diode by means of a multi-band Wigner transport model. Furthermore we will apply multiband
quantum kinetic model to study high field effects in carbon nanotubes and in graphene structures.
Graphene is an interesting material for future device applications not only because of its greatly enhanced mobility compared to traditional transistor materials but
especially due to its unique band structure. In the proximity of the Fermi energy, the bands are well described by a biconical shape, resembling the dispersion relation
of mass less Dirac fermions and thus resulting in unusual effects like the Klein paradox.
Since graphene is essentially a zero band gap material, interband tunneling plays a crucial role. Therefore, a full quantum mechanical treatment has to be carried out. This is done in the framework of the Wigner function formalism.
In this work, two different cases are examined: On the one hand, the full non-local time evolution equations for the Wigner function to study Klein tunneling and on the other
hand, in the limit of larger device dimensions (submicrometer) and slowly varying electric fields, a set of approximate equations of motion is considered. The latter is in
close analogy to its semi-classical counterpart with extra terms incorporating the quantum mechanical corrections.

By means of a two-dimensional drift-diffusion approach we investigate the principle mechanisms which
influence the shape of the I-V characteristic of top-contact bottom-gate pentacene thin-film transistors.
Recent calculations deal with the charge carrier injection mechanisms present at the contacts, the formation
of a hysteresis in the transfer characteristic due to trapping and detrapping of charge carriers, and the influence of light.

The aim of this work is to study the impact of built-in electric fields on the carrier transport and the efficiency of nanocomposite solar cells by means of
numerical modeling. A two-dimensional drift-diffusion model is used to describe carrier transport in the devices. Novel strategies will be tested to incorporate
electric fields due to charge rearrangements at metal-semiconductor or semiconductor-semiconductor interfaces into the model. The such developed model will be
used to quantitatively study the device efficiency as a function of origin, position, and extent of such electric fields.